Starting internal combustion engines usually requires the use of a choke system of some type. Choke systems typically perform the fuel mixture adjustments necessary to start a cold engine. When the fuel-air mixture is too cold, the engine will usually not start properly, or will start and stall out periodically. When engaged (closed), the choke system usually causes the fuel-air mixture to be increased, or “enriched” as the choke is a special valve placed at the mouth of the carburetor for partially blocking off the entering air. When the choke system is in a closed position, the fuel system of the cold engine has a very high restriction on the air intake. The restriction of the air intake forms a vacuum communicating with the fuel line, drawing more fuel into the engine via the carburetor from the fuel bowl or tank. This rich fuel mixture burns even at cool temperatures, allowing the engine to start and warm up. As the engine begins to warm, a certain amount of air is necessary to keep the engine running. If the choke is not opened and air does not begin to enter the fuel system, the engine will likely run for only a short period of time and then will stall. This start and stall process is commonly known as a “false start”. The reason for the “false start” is that as the speed of the engine increases, the engine draws in more fuel. With the choke in the closed position, however, the amount of airflow entering the engine is not increased. Thus a proper mixture of air and fuel is not achieved and the engine will subsequently stall. Moreover, if the engine does not start immediately, a substantial amount of fuel is sucked into the engine, via the carburetor, causing the engine to become flooded, further hampering the starting procedure of the engine.
Older choke systems typically focus on manual choke valves in which the user of the engine would manually close the choke when starting the engine. With manual choke valves, the user must open the choke valve quickly after the engine begins running to avoid the engine false starting. A further problem of manual choke valves is that a user often does not open the valve fully, resulting in a rich fuel mixture. This rich fuel mixture causes carbon to form in the combustion chambers and on the spark plugs. To solve these problems, automatic choke valves were developed to automatically open the choke valve based on engine heat, speed, vibrations, or vacuums.
Several automatic choke valves have been developed that rely on engine temperature. One such choke valve can be found in U.S. Pat. No. 4,348,996 to Morozumi. This type of choke valve is run by a thermostat that is controlled by exhaust heat. When an engine is cold, the valve will be closed for starting. As the engine warms, the exhaust heat will gradually open the choke valve. An automatic choke based on engine temperature depends on a thermostatic coil spring unwinding as heat is supplied. As the engine warms up, manifold heat is transmitted to the choke housing causing the spiral bimetal element to relax, thus opening the valve.
Other automatic choke valves have been developed that will open the choke valve based on engine vibrations or engine speed. U.S. Pat. No. 4,820,454 to Scott et al. discloses a choke assembly that utilizes the vibration of the internal combustion engine during start up for enabling air to enter into the carburetor of the engine at startup. The invention disclosed in Scott et al. describes an inertia valve that is resiliently biased in the bore of an engine that is responsive to vibration of the engine for providing a controlled amount of combustion air into the carburetor of the engine. U.S. Pat. No. 4,298,549 to Woodworth discloses a choke valve that is biased closed with a spring and is then opened based on engine speed vacuum.
A further type of automatic choke valve developed is based upon the vacuum created within an engine compartment as an engine is started and begins to run. U.S. Pat. No. 3,928,511 to Atsumi et al. discloses a vacuum-operated choke valve for the air intake passage of an internal combustion engine. When a user desires to start a cold engine, he pulls a manual knob, which through various linkages closes the choke valve. When the engine starts, the vacuum from the engine moves the connecting rod to the right, thereby opening the choke valve. The choke valve is biased by a spring to the actuator so that the force of the spring increases as the actuator is moved beyond the position corresponding to the closed position of the choke valve.
U.S. Pat. No. 4,951,926 to O'Shea et al. discloses a choke system in which the choke valve is biased in a direction to block the passage of air between the air inlet and the air outlet of the choke housing. The choke valve is responsive to engine vacuum during starting of the engine to move the valve in a direction against the biasing element to permit air to enter the carburetor from outside the housing. Finally, U.S. Pat. No. 5,194,186 to Edlund discloses a carburetor provided with an elastic choke valve that will yield to the air stream created by an engine vacuum and furnish a fuel-air mixture to the engine. The choke valve of Edlund begins in a closed position and when the engine is started and a vacuum in the engine compartment is created, there will be a force of air to pass around the choke valve. The elastomer choke valve is permitted to bend to a partially open position until the user can manually open the choke to a fully opened position.
Despite the existence of automatic choke valves based upon different engine operating parameters, it is desirable to provide a novel choke system and method that can be vacuum-operated and which overcomes disadvantages of the prior art choke systems.